On Thu, Jan 27, 2022 at 03:26:43PM +0100, Thomas Zimmermann wrote:
Hi
Am 26.01.22 um 21:36 schrieb Lucas De Marchi:
In certain situations it's useful to be able to read or write to an offset that is calculated by having the memory layout given by a struct declaration. Usually we are going to read/write a u8, u16, u32 or u64.
Add a pair of macros dma_buf_map_read_field()/dma_buf_map_write_field() to calculate the offset of a struct member and memcpy the data from/to the dma_buf_map. We could use readb, readw, readl, readq and the write* counterparts, however due to alignment issues this may not work on all architectures. If alignment needs to be checked to call the right function, it's not possible to decide at compile-time which function to call: so just leave the decision to the memcpy function that will do exactly that on IO memory or dereference the pointer.
Cc: Sumit Semwal sumit.semwal@linaro.org Cc: Christian König christian.koenig@amd.com Cc: linux-media@vger.kernel.org Cc: dri-devel@lists.freedesktop.org Cc: linaro-mm-sig@lists.linaro.org Cc: linux-kernel@vger.kernel.org Signed-off-by: Lucas De Marchi lucas.demarchi@intel.com
include/linux/dma-buf-map.h | 81 +++++++++++++++++++++++++++++++++++++ 1 file changed, 81 insertions(+)
diff --git a/include/linux/dma-buf-map.h b/include/linux/dma-buf-map.h index 19fa0b5ae5ec..65e927d9ce33 100644 --- a/include/linux/dma-buf-map.h +++ b/include/linux/dma-buf-map.h @@ -6,6 +6,7 @@ #ifndef __DMA_BUF_MAP_H__ #define __DMA_BUF_MAP_H__ +#include <linux/kernel.h> #include <linux/io.h> #include <linux/string.h> @@ -229,6 +230,46 @@ static inline void dma_buf_map_clear(struct dma_buf_map *map) } } +/**
- dma_buf_map_memcpy_to_offset - Memcpy into offset of dma-buf mapping
- @dst: The dma-buf mapping structure
- @offset: The offset from which to copy
- @src: The source buffer
- @len: The number of byte in src
- Copies data into a dma-buf mapping with an offset. The source buffer is in
- system memory. Depending on the buffer's location, the helper picks the
- correct method of accessing the memory.
- */
+static inline void dma_buf_map_memcpy_to_offset(struct dma_buf_map *dst, size_t offset,
const void *src, size_t len)+{
- if (dst->is_iomem)
memcpy_toio(dst->vaddr_iomem + offset, src, len);- else
memcpy(dst->vaddr + offset, src, len);+}
Please don't add a new function. Rather please add the offset parameter to dma_buf_map_memcpy_to() and update the callers. There are only two calls to dma_buf_map_memcpy_to() within the kernel. To make it clear what the offset applies to, I'd call the parameter 'dst_offset'.
+/**
- dma_buf_map_memcpy_from_offset - Memcpy from offset of dma-buf mapping into system memory
- @dst: Destination in system memory
- @src: The dma-buf mapping structure
- @src: The offset from which to copy
- @len: The number of byte in src
- Copies data from a dma-buf mapping with an offset. The dest buffer is in
- system memory. Depending on the mapping location, the helper picks the
- correct method of accessing the memory.
- */
+static inline void dma_buf_map_memcpy_from_offset(void *dst, const struct dma_buf_map *src,
size_t offset, size_t len)+{
- if (src->is_iomem)
memcpy_fromio(dst, src->vaddr_iomem + offset, len);- else
memcpy(dst, src->vaddr + offset, len);+}
With the dma_buf_map_memcpy_to() changes, please just call this function dma_buf_map_memcpy_from().
/**
- dma_buf_map_memcpy_to - Memcpy into dma-buf mapping
- @dst: The dma-buf mapping structure
@@ -263,4 +304,44 @@ static inline void dma_buf_map_incr(struct dma_buf_map *map, size_t incr) map->vaddr += incr; } +/**
- dma_buf_map_read_field - Read struct member from dma-buf mapping with
- arbitrary size and handling un-aligned accesses
- @map__: The dma-buf mapping structure
- @type__: The struct to be used containing the field to read
- @field__: Member from struct we want to read
- Read a value from dma-buf mapping calculating the offset and size: this assumes
- the dma-buf mapping is aligned with a a struct type__. A single u8, u16, u32
- or u64 can be read, based on the offset and size of type__.field__.
- */
+#define dma_buf_map_read_field(map__, type__, field__) ({ \
- type__ *t__; \
- typeof(t__->field__) val__; \
- dma_buf_map_memcpy_from_offset(&val__, map__, offsetof(type__, field__), \
sizeof(t__->field__)); \- val__; \
+})
+/**
- dma_buf_map_write_field - Write struct member to the dma-buf mapping with
- arbitrary size and handling un-aligned accesses
- @map__: The dma-buf mapping structure
- @type__: The struct to be used containing the field to write
- @field__: Member from struct we want to write
- @val__: Value to be written
- Write a value to the dma-buf mapping calculating the offset and size.
- A single u8, u16, u32 or u64 can be written based on the offset and size of
- type__.field__.
- */
+#define dma_buf_map_write_field(map__, type__, field__, val__) ({ \
- type__ *t__; \
- typeof(t__->field__) val____ = val__; \
- dma_buf_map_memcpy_to_offset(map__, offsetof(type__, field__), \
&val____, sizeof(t__->field__)); \+})
As the original author of this file, I feel like this shouldn't be here. At least not until we have another driver using that pattern.
Let me try to clear out the confusion. Then maybe I can extend the documentation of this function in v2 if I'm able to convince this is useful here.
This is not about importer/exporter, having this to work cross-driver. This is about using dma_buf_map (which we are talking about on renaming to iosys_map or something else) for inner driver allocations/abstractions. The abstraction added by iosys_map helps on sharing the same functions we had before. And this macro here is very useful when the buffer is described by a struct layout. Example:
struct bla { struct inner inner1; struct inner inner2; u32 x, y ,z; };
Functions that would previously do:
struct bla *bla = ...;
bla->x = 100; bla->y = 200; bla->inner1.inner_inner_field = 30;
Can do the below, having the system/IO memory abstracted away (calling it iosys_map here instead of dma_buf_map, hopeful it helps):
struct iosys_map *map = ...;
iosys_map_write_field(map, struct bla, x, 100); iosys_map_write_field(map, struct bla, y, 200); iosys_map_write_field(map, struct bla, inner1.inner_inner_field, 30);
When we are using mostly the same map, the individual drivers can add quick helpers on top. See the ads_blob_write() added in this series, which guarantees the map it's working on is always the guc->ads_map, while reducing verbosity to use the API. From patch "drm/i915/guc: Add read/write helpers for ADS blob":
#define ads_blob_read(guc_, field_) \ dma_buf_map_read_field(&(guc_)->ads_map, struct __guc_ads_blob, \ field_)
#define ads_blob_write(guc_, field_, val_) \ dma_buf_map_write_field(&(guc_)->ads_map, struct __guc_ads_blob,\ field_, val_)
So in intel_guc_ads, we can have a lot of:
- bla->x = 100; + ads_blob_write(guc, x, 10);
thanks Lucas De Marchi